1. Field of the Invention
The present invention relates generally to gas-mixing systems and, more particularly, to an improved radially designed gas manifold characterized by precise mixing and accurate admission of a plurality of gases into a processing chamber, as well as by rapid switching among the gases, yet occupying a minimum of dead space.
2. The Prior Art
Gas manifolds are used in gas-mixing system. A manifold is a linear assembly, such as a pipe fitting, with a plurality of valved inlets for connecting a plurality of fluid lines to a single processing chamber (i.e., several engine cylinders to a carburator), or for connecting one fluid line with a plurality of fluid outlet lines (as in a water distribution system). In the former, i.e., in the gathering of multipleline fluid inputs into a single intake chamber, the manifold is known as an intake manifold; and in the latter, i.e., in the division of a single fluid supply in several outlet streams, the manifold is described as a distribution manifold.
The invention herein primarily relates to an intake manifold, although it could be adapted, with modifications not disclosed herein, to distribution manifolds as well. Specifically, the invention relates to a gas intake manifold as used in industry. One such industrial use includes the semiconductor industry. specifically one involving the manufacture of high performance electronic and optoelectronic devices by epitaxial growth of compound semiconductors utilizing organometallic compounds. Such systems employ reaction chambers for metalorganic chemical vapor deposition (MOCVD) and gas-mixing systems to feed those chambers. In such systems, the flow of the several gases must be optimized and the manifold must be capable of achieving abrupt transitions among the several gases to effect the required changes between the deposited layers. One such CVD Reaction Chamber is disclosed in U.S. Pat. No. 4,596,208 granted to Spire Corporation, the common assignee herein, on June 24, 1986, the disclosure of which is incorporated herein by reference. In this patent, U.S. Pat. No. 4,596,208, a conventional linear assembly intake manifold is used. As such, the several gases are entering the manifold at different distances along the axial length of the manifold. Valving of gases into such linear manifold results either in an abrupt flow of the just valved gas or in non-uniform flow thereof until such time that a constant flow rate is reached. The time interval for the newly valved gas to reach its desired constant rate flow, however finite, does nevertheless adversly affect the deposition process. Further, gases admitted into the linear manifold farthest from the gas processing chamber have, of necessity, a longer distance to cover in the manifold than do gases valved thereto at points closer to the gas processing chamber. Consequently, great care must be exercised in adjusting the respective times for opening and closing the respective valves so as to achieve the desired confluence of the gases in the manifold before such gases do reach the gas processing chamber. Maintenance of such a linearly valved manifold system also is troublesome, requiring frequent cleaning and dismounting of the valves.